GRE Subject Test: Biochemistry, Cell, and Molecular Biology : Help with Other Laboratory Techniques

Study concepts, example questions & explanations for GRE Subject Test: Biochemistry, Cell, and Molecular Biology

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All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources

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Example Questions

Example Question #1 : Help With Other Laboratory Techniques

What is the purpose of adding sodium fluoride to a cell lysis buffer?

Possible Answers:

It is a serine/threonine phosphatase inhibitor

It is a serine protease inhibitor

It is a cysteine protease inhibitor

It is a tyrosine phosphatase inhibitor

Correct answer:

It is a serine/threonine phosphatase inhibitor

Explanation:

Sodium fluoride is a serine/threonine phosphatase inhibitor. This is important to have in a cell lysis buffer if the protein of interest is phosphorylated. The presence of sodium fluoride will prevent the phosphoryl group from being removed by a serine/threonine phosphatase before it can be studied. It is often added to the cell lysis buffer along with sodium vanadate, which is a tyrosine/alkaline phosphatase inhibitor.

Example Question #2 : Help With Other Laboratory Techniques

Which of the following techniques would best determine relative protein activity by its ability to bind specific DNA sequences in vitro?

Possible Answers:

Co-immunoprecipitation

Electrophoretic mobility shift assay (EMSA)

Western blot

Chromatin immunoprecipitation (ChIP)

Bradford protein assay

Correct answer:

Electrophoretic mobility shift assay (EMSA)

Explanation:

The correct answer is electrophoretic mobility shift assay (EMSA). In an EMSA, specific DNA sequences are radioactively labelled and incubated with either protein lysates or purified proteins. The protein-DNA mixture is then loaded onto a non-denaturing gel to separate the proteins and DNA by size. DNA that is bound by protein will migrate more slowly than unbound DNA, which will migrate quickly. To detect radioactivity, a film is exposed to the gel, developed and interpreted. It is important to remember that the radioactivity is emitted by the DNA and not the protein.

Example Question #3 : Help With Other Laboratory Techniques

Two students have cloned a bacterial DNA polymerase into a mammalian expression vector. The students then transfected the vector into human tissue culture cell lines to determine if the DNA polymerase retains its native function in human cells.

What technique is most suitable for the students to use to determine if the DNA polymerase is expressed in human cells?

Possible Answers:

Western blot

Electrophoretic mobility shift assay (EMSA) 

Restriction digestion

Electroporation

Polymerase chain reaction (PCR)

Correct answer:

Western blot

Explanation:

The correct answer is Western blot. In a Western blot, cell protein lysates are run on a denaturing gel and probed with a specific antibody. The student researchers can detect the existence of the DNA polymerase protein in the cell lysate using a specific antibody to that polymerase.

EMSAs determine a protein's ability to bind a DNA sequence, while electroporation, PCR, and restriction digests are not methods to detect protein expression. 

Example Question #71 : Gre Subject Test: Biochemistry, Cell, And Molecular Biology

What technique allows scientists to measure gene expression via probe-cDNA hybridization fluorescent intensity? 

Possible Answers:

DNA microarray

Fluorescence-activated cell sorting (FACS)

Immunohistochemistry

Karyotype

In situ hybridization (ISH)

Correct answer:

DNA microarray

Explanation:

The correct answer is DNA microarray. In a DNA microarray, short DNA sequences (probes) are labelled on a microarray chip. Probes for the same gene are clustered in the same area on the array. cDNA from a sample is labelled with a fluorescent dye and washed over the chip. If a certain gene is more highly expressed, its cDNA will bind the respective probes and give a higher intensity than a lower expressed gene. 

Example Question #4 : Help With Other Laboratory Techniques

A student researcher performs indirect immunofluorescence of mammalian cells for a transmembrane protein with an antibody to the C-terminus of the protein. First, the student researcher does not permeabilize cells' plasma membranes and stains with the protein specific antibody. Secondly, the researcher permeabilizes the cells' plasma membranes and stains with the protein specific antibody. 

What is the student researcher trying to determine with these two experiments? 

Possible Answers:

If the protein is localized to the Golgi apparatus

Whether the cells can survive permeabilization 

If the protein is localized to the Golgi apparatus

Whether the protein localization is disrupted when the plasma membrane is permeabilized

Whether the C-terminus of the protein is extracellular or intracellular

Correct answer:

Whether the C-terminus of the protein is extracellular or intracellular

Explanation:

The correct answer is whether the C-terminus of the protein is extracellular or intracellular. This is a very common laboratory technique to determine which terminus of a transmembrane protein is intracellular and extracellular. Since the antibody is specific to the C-terminus of the protein and if the C-terminus of the protein is intracellularly localized, we will only be able to detect the protein if the cells are permeabilized. In cells that are not permeabilized, the antibody will not be able to enter the cells, but permeabilization will allow the antibody to pass through the plasma membrane and bind the C-terminus. If the C-terminus is extracellular, the antibody will bind regardless of permeabilization.  

Example Question #73 : Gre Subject Test: Biochemistry, Cell, And Molecular Biology

Which of the following is not a valid method to introduce exogenous DNA into a cell? 

Possible Answers:

None of these

Infection 

Electroporation 

Transformation

Transfection 

Correct answer:

None of these

Explanation:

All of the given answers are valid methods to introduce exogenous DNA into a cell. When working with bacteria, transformations are a simple way to introduce plasmid DNA into the cell by chemical competency. Electroporation electrocutes both bacterial and cell culture cells to introduce exogenous DNA. Infection of target cells may also be a viable method if the laboratory is equipped to generate live virus containing exogenous DNA to be introduced. Finally, transfection refers to a process mainly reserved for cell culture that introduces exogenous DNA through liposome fusion (containing DNA) with cell membranes. 

Example Question #74 : Gre Subject Test: Biochemistry, Cell, And Molecular Biology

Work on the Anopheles mosquito attempting to study the blood digestion process found that over 2,000 genes were upregulated and downregulated through digestion. What technology makes it possible to study expression levels of large number of genes like this?

Possible Answers:

Next generation DNA sequencing

DNA microarrays

None of these

Polymerase chain reaction

Sanger DNA sequencing

Correct answer:

DNA microarrays

Explanation:

Microarrays allow for the study of expression levels of thousands of genes simultaneously. Although microarrays do not tell you anything about the actual sequence of the genes, they are the only option for studying the expression levels of massive numbers of genes. It is possible to study expression levels using PCR, but not on a large scale.

Example Question #75 : Gre Subject Test: Biochemistry, Cell, And Molecular Biology

What was the early technique used in molecular genetics to study "alleles" of various enzymes?

Possible Answers:

Allozyme gels

Isozyme gels

None of these

Northern blots

Isoenzymatic gels

Correct answer:

Allozyme gels

Explanation:

Running allozyme gels was one of the first methods used in molecular studies of these enzymes that have slightly different functions due to having slightly different genetic codes (alleles). This term refers specifically to enzymatic variation created by genetic variation/alleles.

Example Question #76 : Gre Subject Test: Biochemistry, Cell, And Molecular Biology

What is the purpose of a phenol/chloroform extraction?

Possible Answers:

To generate a protein lysate from tissue culture cells by lysing 

To separate proteins and other impurities from DNA or RNA 

To separate DNA and RNA from proteins 

To separate euchromatin from heterochromatin in cell lysates

None of the other answers 

Correct answer:

To separate proteins and other impurities from DNA or RNA 

Explanation:

The correct answer is to separate proteins and other impurities from DNA or RNA. An extraction by phenol followed by chloroform will separate proteins and other impurities from DNA and RNA (in suspended fraction). Next, depending on the type and concentration of salt used, a researcher can selectively precipitate either DNA or RNA from the mixture with the addition of ethanol. This is a simple method to obtain pure clean ribonucleic acids from impure sources. 

Example Question #77 : Gre Subject Test: Biochemistry, Cell, And Molecular Biology

Which of the following techniques most likely utilizes a detergent, such as sodium dodecyl sulfate? 

Possible Answers:

Lysis of the plasma membrane 

None of the other answers

Purification of DNA from RNA and proteins 

Separation of small and large ionic compounds 

All of these require utilization of a detergent

Correct answer:

Lysis of the plasma membrane 

Explanation:

The correct answer is lysis of the plasma membrane. While detergents such as sodium dodecyl sulfate are commonly used in western blots as a protein denaturing agent, it also breaks down the plasma membrane by emulsifying membrane-bound lipids and proteins.  

All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources

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